The dehydrogenation of hydrocarbons is an important commercial hydrocarbon conversion process because of the existing and growing demand for dehydrogenated hydrocarbons for the manufacture of various chemical products such as detergents, high octane gasolines, oxygenated gasoline blending components, pharmaceutical products, plastics, synthetic rubbers and other products which are well known to those skilled in the art. One example of this process is the dehydrogenation of isobutane to produce isobutylene which can be polymerized to provide tackifying agents for adhesives, viscosity-index additives for motor oils and impact-resistant and anti-oxidant additives for plastics. Another example of the growing demand for isobutylene is the production of oxygen-containing gasoline blending components which are being mandated by the government in order to reduce air pollution from automotive emissions.
Those skilled in the art of hydrocarbon conversion processing are well versed in the production of olefins by means of catalytic dehydrogenation of paraffinic hydrocarbons. In addition, many patents have issued which teach and discuss the dehydrogenation of hydrocarbons in general. For example, U.S. Pat. No. 4,430,517 issued to Imai et al discusses a dehydrogenation process and catalyst for use therein.
Despite the fact that the dehydrogenation of paraffinic hydrocarbons is well known, the more widespread usage of this processing technology and greater severity operation of existing commercial facilities has highlighted the problem which occurs in the product recovery section of hydrocarbon dehydrogenation processes. This problem is the result of the co-production of trace quantities of mononuclear aromatic and polynuclear aromatic compounds. The mononuclear aromatic compounds are considered to be an undesired impurity in the desired olefinic hydrocarbon product stream and must be removed. The polynuclear aromatic compounds are not only an undesired impurity, but also present a severe operational problem because when they condense and plate out on the cooler surfaces of the plant there are detrimental results. The deposits of polynuclear aromatic compounds are difficult to remove, they reduce the efficiency of heat exchangers and they may eventually lead to plugging.
Therefore, those skilled in the art of hydrocarbon processing have sought methods to overcome the problem posed by the production of polynuclear aromatic compounds in dehydrogenation production facilities. Previous solutions to this problem have centered on recovering low molecular weight mononuclear aromatic hydrocarbon compounds from the dehydrogenation effluent and recycling these hydrocarbon compounds as a wash solvent. A drawback to this technique is that low molecular weight mononuclear aromatic hydrocarbon compounds cannot be easily separated from the normally gaseous hydrocarbon product without using high pressure or low temperature separation. Without high pressure or low temperature separation, significant quantities of wash solvent containing low molecular weight mononuclear aromatic hydrocarbon compounds will be carried forward through the compressor from the wash section thereby adding an additional load to the compressor.